US4748414A - Nuclear spin tomograph - Google Patents

Nuclear spin tomograph Download PDF

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Publication number
US4748414A
US4748414A US06/835,865 US83586586A US4748414A US 4748414 A US4748414 A US 4748414A US 83586586 A US83586586 A US 83586586A US 4748414 A US4748414 A US 4748414A
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US
United States
Prior art keywords
test
cavity
field
coil
magnet
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Expired - Fee Related
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US06/835,865
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English (en)
Inventor
Bertold Knuttel
Gunther R. Laukien
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Bruker Biospin MRI GmbH
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Bruker Medizintechnik GmbH
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Assigned to BRUKER MEDIZINTECHNIK GMBH reassignment BRUKER MEDIZINTECHNIK GMBH ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: KNUTTEL, BERTOLD, LAUKIEN, GUNTHER R.
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/381—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field using electromagnets
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/387—Compensation of inhomogeneities
    • G01R33/3873—Compensation of inhomogeneities using ferromagnetic bodies ; Passive shimming
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/42—Screening
    • G01R33/421—Screening of main or gradient magnetic field
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F7/00—Magnets
    • H01F7/06—Electromagnets; Actuators including electromagnets
    • H01F7/20—Electromagnets; Actuators including electromagnets without armatures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3806—Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets

Definitions

  • the present invention proceeds from a nuclear spin tomograph comprising a magnet system with a, preferably, elongated holder for a test object arranged in its one axis to slide in a longitudinal direction, the test object being further surrounded by coil systems. for generating gradient fields and for irradiating a radio-frequency field.
  • nuclear spin tomography or NMR tomography is understood to describe a method in which a test object, in particular a live human body or animal body is subjected simultaneously to a strong homogenous magnetic field and an r.f. field directed perpendicularly thereto. At the same time, one generates in the area of the test object a gradient field acting in the same direction as the homogenous magnetic field and decreasing in strength in the axis of the test object.
  • the r.f. field when the r.f. field is applied, nuclear magnetic resonance occurs only in the area of one plane of the test object because, due to the active gradient field, the magnetic field has a strength which, given the gyromagnetic ratio of protons, corresponds to the frequency of the irradiated r.f. field only in the area of this same plane. This makes it possible to produce sectional images of the test object.
  • the extreme homogeneity of the magnetic field required in the sample space is impaired already by minor disturbing factors occurring outside the magnetic system.
  • Such disturbing factors may be either of a stationary nature, as for example reinforcing steel in the walls of the room in which the nuclear spin tomograph is installed, or else of a moving type, such as instrument trolleys moved in the neighborhood of the tomograph or even cars passing outside the examination building.
  • air-cored coils give rise to a considerable leakage field since the homogenous magnetic field extending along the axis of the air-cored coil closes via the external space of the air-cored coil.
  • This leakage field of the air-cored coil may influence equipment placed near the magnet system, such as electronic equipment, data processing systems or radiological equipment in a hospital.
  • the leakage field may also disturb the operation of pacemakers so that it may be connected with certain risks for pacemaker patients to stay near the magnet system.
  • German Disclosure Document No. 31 23 493 has been provided with a shielding of a soft-magnetic material which absorbs the largest part of the leakage field. But due to the solenoid design of the air-cored coil, in which the direction of the constant magnetic field coincides with the coil axis, a considerable portion of the leakage field is still permitted to leak out through the opening which is required for introducing the test object.
  • magnet systems using air-cored coil arrangements in the form of Helmholtz arrangements or of solenoids are connected with still another disadvantage resulting from the coil geometry.
  • the constant magnetic field extends in the case of these coils along the direction of the coil axis and, thus, also the longitudinal axis of the patient.
  • the coils required for irradiating the r.f. field therefore have to be of the saddle-shaped type as the r.f. field must extend perpendicularly to the constant magnetic field.
  • these saddle-shaped r.f. coils which serve not only for radiating the r.f. field, but also for receiving the measuring signal, have a relatively poor efficiency which in practice is lower by the factor 2.5 than the one that can be achieved with the aid of an r.f. transmitting and receiving coil in the form of a solenoid.
  • normally conductive air-cored systems offer the known disadvantage that the conversion ratio, i.e. the ratio between the achieved field strength and the consumed electric energy, is relatively poor so that large power supplies with a considerable energy consumption are required for feeding such normally conductive air-cored coil systems.
  • this object is achieved by an arrangement in which the magnet system is provided with a yoke iron body enclosing a longitudinal opening for receiving the test object, with outer marginal areas of the longitudinal opening accommodating coil sections which extend in the direction of the longitudinal opening, which are bent over at the ends thereof and which close above the opening.
  • the tomograph according to the invention offers the advantage that any magnetic disturbing factors acting from the outside to the inside or from the inside to the outside are largely suppressed by the use of an iron body which is closed almost all round and in which the magnetic field closes passing only an air space which is intended for receiving the test object and which is enclosed by the iron body over the whole longitudinal area.
  • the constant magnetic field present in the air space is delimited by level iron faces so that solenoid-shapped r.f. coil arrangements may be used which permit an improved signal yield to be achieved.
  • the ferromagnetic system employed according to the invention permits the use of power supplies of a lower rating as systems of this type are generally known to achieve higher field strengths with lower energy consumption.
  • one pair of coil sections is arranged in each corner of the longitudinal opening which exhibits a rectangular cross-sectional shape.
  • This arrangement facilitates the process of winding the necessary coils and in particular bending over the coils in the area of the outer openings.
  • a rectangular cross-sectional shape of the longitudinal opening provides already good basic homogeneity of the magnetic field, without the use of any additional aids.
  • such a longitudinal opening also facilitates the use of displaceable stretchers for the patients to be examined.
  • a particularly favorable effect is achieved in this arrangement when the described coil sections can be displaced, preferably in two directions perpendicular to the axis of the longitudinal opening.
  • the possibility to displace the coil sections in this manner provides a very simple means of improving the homogeneity of the magnetic field.
  • a further improvement of the homogeneity of the field can be achieved according to the invention by arranging longitudinal shims in the form of ferromagnetic sections in the longitudinal opening, for field correction. These sections may be arranged either in the marginal area of the opening to compensate for marginal field losses, or else in the middle of the opening to compensate for a possible field drop in the central area.
  • Suitable homogenization of the magnetic field is further possible by arranging in the inner marginal area of the iron body a soft-magnetic plate which delimits the longitudinal opening and which can be displaced, by means of suitable adjusting means, in at least one direction perpendicular to the axis of the longitudinal opening.
  • suitable adjusting means for adjusting the homogeneity of the field are obtained, for example, by the use of a spindle.
  • the iron body is provided with soft-magnetic cover plates closing the longitudinal opening, leaving open substantially only the area through which the coil sections project outwardly and, preferably, an opening for the introduction of the test object, and extending a certain way into the marginal area of the iron body adjacent the longitudinal opening.
  • the magnet system used may, according to a further improvement of the invention, be arranged in such a manner that the test object, in particular a patient, can be introduced into the magnet system in horizontal position; it is, however, also possible to provide the magnet system in upright arrangement, i.e. with its axis extending in the vertical direction relative to the surrounding space, so that the patient can be examined either standing or in seated position.
  • FIG. 1 is a perspective view of part of one embodiment of a nuclear spin tomograph according to the invention
  • FIG. 2 is a diagrammatic front view of a magnet system employed according to the invention.
  • FIG. 3 is a view corresponding to FIG. 2, showing different means for correcting the magnetic field
  • FIG. 4 shows a representation corresponding to FIG. 2, but with shielding cover plates.
  • an iron body 10 of cuboid shape comprises a full-length coaxial longitudinal opening 11 of rectangular cross-section.
  • the axis of the longitudinal opening 11 is designated by the letter x
  • the axes extending vertically thereto are designated by z and y.
  • the axes x and y extend in the horizontal, the axis z in the vertical direction, relative to the surrounding space.
  • this is the case only in the embodiment shown in FIG. 1, it being of course also possible to orient the arrangement of FIG. 1 differently, for example in such a manner that the axis x extends vertically relative to the surrounding space so that a patient can be examined in standing or seated position, as described in detail in the before-mentioned German Disclosure Document No. 31 23 493.
  • the longitudinal opening 11 contains a total of four coil sections, with flat coils 12 and 12' extending in the upper corners of the rectangular longitudinal opening 11, and flat coils 13 and 13' extending in the lower corners.
  • the flat coils 12 and 13 are bent off at the points 14 and 15 initially by 90° in the y direction and then upwardly by 180° in the z direction, extending thereafter along the end faces 16 and 17 in y direction to joint the coil sections 12' and 13'.
  • the flat coils are provided in corresponding arrangement.
  • the described arrangement is to be understood only as an example. It goes without saying that only a single pair of coils or a greater number of pairs of coils may be used instead of the two pairs of coils 12, 12' and 13, 13' shown in FIG. 1.
  • the coil section 12 projecting from the opening may, for example, be bent off initially by 90° in the upward direction and then bent over by 90° in the y direction.
  • a support 18 can be seen carrying guide means 19 for a stretcher 20.
  • the stretcher 20 serves for receiving a test object, for example a patient, and can be moved in the x direction into the longitudinal opening 11.
  • FIG. 2 is a simplified front view of the representation according to FIG. 1 showing again the iron body 10 containing the longitudinal opening 11 and the pairs of coils 12, 12' and 13, 13' closing in the manner described above via the portions 14, 15, 16, 17.
  • the before-mentioned coils generate a magnetic field extending very homogenously over the space of the longitudinal opening 11 between cover faces 28 and 29 and closing on the outside via the side walls of the iron body 10.
  • This constant magnetic field generated by the coil system 12, 13 is indicated in FIG. 2 by reference numeral 30. It passes the test object 31 arranged on the stretcher 20 in the manner indicated in the drawing, i.e. a patient stretched out on the stretcher 20 in an axis extending vertically relative to his longitudinal axis.
  • An r.f. coil 32 provided for irradiating the required r.f. field lays a plane in the z y direction in the embodiment shown in FIG. 2. It is, however, understood that contrary to the representation shown in FIG. 2, the coil 32 may also be arranged in a position rotated by 90° in which case it would lay a plane in the z x direction.
  • FIG. 3 which corresponds to the view of FIG. 2, individual means for correcting the magnetic field are indicated.
  • the coils 12, 12', 13, 13' may be arranged for displacement in the directions 40, 41, i.e. in the y and z directions. It is, however, also possible to provide so-called longitudinal shims 42, 44, 45 substantially in the form of ferromagnetic sections, preferably rectangular sections, extending in the x direction in the longitudinal opening 11. These shims 42, 44, 45 may be displaceable in a direction 43, i.e. in the y direction.
  • the soft iron plate 46 is received in a recess 47 in the top face 28 or the bottom face 29 and can be displaced in a direction 49 along the z axis, for example by means of a spindle indicated at 48.
  • the coils 12, 13 may also be provided with correction coils 50, 51 which are superimposed upon the coils 12, 13 in the z or the y direction.
  • the inner space is already largely shielded due to the particular structure of the iron body 10 which encloses the longitudinal opening 11 almost completely, so that on the one hand no disturbing factors are permitted to penetrate from the outside to the inside while on the other hand no leakage fields emanating from the magnet system can influence any equipment outside the magnetic system.
  • a further improvement of the invention according to FIG. 4 provides that the longitudinal opening 11 can be closed on one side or on both sides by a cover plate 60 leaving open only the areas where the coils 12, 12' and 13, 13' project from the opening.
  • Marginal portions 62, 63 of the cover plate 60 extend a certain way into the end faces of the iron body 10 so that the field lines of any residual leakage field are closed safely.
  • the cover plate 60 may be provided on one side or on both sides with an opening 61 of a size permitting the test object 31 to be introduced lying on the stretcher 20.
  • FIG. 4 is of a diagrammatic nature only and that all hinges, or the like, for the cover plate 60 have been omitted for greater clarity.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Epidemiology (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
US06/835,865 1984-05-19 1985-05-15 Nuclear spin tomograph Expired - Fee Related US4748414A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19843418812 DE3418812A1 (de) 1984-05-19 1984-05-19 Kernspintomograph
DE3418812 1984-05-19

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EP (1) EP0181383B1 (de)
DE (2) DE3418812A1 (de)
WO (1) WO1985005448A1 (de)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4849727A (en) * 1986-11-13 1989-07-18 Kabushiki Kaisha Toshiba Magnetic shield for a magnetic resonance magnet
US4998976A (en) * 1987-10-07 1991-03-12 Uri Rapoport Permanent magnet arrangement
US5063934A (en) * 1987-10-07 1991-11-12 Advanced Techtronics, Inc. Permanent magnet arrangement
WO1994007250A1 (en) * 1992-09-11 1994-03-31 Magna-Lab Inc. Permanent magnetic structure
US5389879A (en) * 1992-12-18 1995-02-14 Pulyer; Yuly M. MRI device having high field strength cylindrical magnet with two axially spaced electromagnets
US5436607A (en) * 1992-08-05 1995-07-25 General Electric Company Open (non-enclosed) magnets for magnetic resonance imaging
EP0883143A1 (de) * 1996-10-30 1998-12-09 Hitachi Medical Corporation Supraleitende magnetische vorrichtung
US20160111192A1 (en) * 2014-10-15 2016-04-21 Vincent Suzara Magnetic field structures, field generators, navigation and imaging for untethered robotic device enabled medical procedure

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4791370A (en) * 1985-08-23 1988-12-13 Resonex, Inc. Gradient field structure and method for use with magnetic resonance imaging apparatus
US4667174A (en) * 1985-08-23 1987-05-19 Resonex, Inc. Magnet assembly for magnetic resonance imaging and method of manufacture
DE3616078A1 (de) * 1986-05-13 1987-11-19 Bruker Analytische Messtechnik Elektromagnetsystem fuer die kernspintomographie
US4766378A (en) * 1986-11-28 1988-08-23 Fonar Corporation Nuclear magnetic resonance scanners
EP0488015B1 (de) * 1990-11-30 1996-10-30 Siemens Aktiengesellschaft Homogenfeldmagnet mit mindestens einer mechanisch auszurichtenden Polplatte

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US4456881A (en) * 1982-01-18 1984-06-26 Technicare Corporation Gradient-coil apparatus for a magnetic resonance system
US4490675A (en) * 1981-06-13 1984-12-25 Bruker Analytische Messtechnik Gmbh Electromagnet for use in NMR tomography
FR2551258A1 (fr) * 1983-08-30 1985-03-01 Cgr Mev Aimant muni de moyens de correction de champ pour creer un champ uniforme
US4613820A (en) * 1984-04-06 1986-09-23 General Electric Company RF shielded room for NMR imaging system

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US3513422A (en) * 1967-03-14 1970-05-19 Newport Instr Ltd Magnet assemblies
US3789832A (en) * 1972-03-17 1974-02-05 R Damadian Apparatus and method for detecting cancer in tissue
US4038622A (en) * 1976-04-13 1977-07-26 The United States Of America As Represented By The United States Energy Research And Development Administration Superconducting dipole electromagnet
US4318043A (en) * 1978-07-20 1982-03-02 The Regents Of The University Of California Method and apparatus for rapid NMR imaging of nuclear densities within an object
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US4442404A (en) * 1978-12-19 1984-04-10 Bergmann Wilfried H Method and means for the noninvasive, local, in-vivo examination of endogeneous tissue, organs, bones, nerves and circulating blood on account of spin-echo techniques
US4490675A (en) * 1981-06-13 1984-12-25 Bruker Analytische Messtechnik Gmbh Electromagnet for use in NMR tomography
US4456881A (en) * 1982-01-18 1984-06-26 Technicare Corporation Gradient-coil apparatus for a magnetic resonance system
FR2551258A1 (fr) * 1983-08-30 1985-03-01 Cgr Mev Aimant muni de moyens de correction de champ pour creer un champ uniforme
US4613820A (en) * 1984-04-06 1986-09-23 General Electric Company RF shielded room for NMR imaging system

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4849727A (en) * 1986-11-13 1989-07-18 Kabushiki Kaisha Toshiba Magnetic shield for a magnetic resonance magnet
US4998976A (en) * 1987-10-07 1991-03-12 Uri Rapoport Permanent magnet arrangement
US5063934A (en) * 1987-10-07 1991-11-12 Advanced Techtronics, Inc. Permanent magnet arrangement
US5436607A (en) * 1992-08-05 1995-07-25 General Electric Company Open (non-enclosed) magnets for magnetic resonance imaging
WO1994007250A1 (en) * 1992-09-11 1994-03-31 Magna-Lab Inc. Permanent magnetic structure
US5623241A (en) * 1992-09-11 1997-04-22 Magna-Lab, Inc. Permanent magnetic structure
US5389879A (en) * 1992-12-18 1995-02-14 Pulyer; Yuly M. MRI device having high field strength cylindrical magnet with two axially spaced electromagnets
EP0883143A1 (de) * 1996-10-30 1998-12-09 Hitachi Medical Corporation Supraleitende magnetische vorrichtung
EP0883143A4 (de) * 1996-10-30 2003-04-02 Hitachi Medical Corp Supraleitende magnetische vorrichtung
US6781492B2 (en) 1996-10-30 2004-08-24 Hitachi Medical Corporation Superconducting magnetic apparatus
US20160111192A1 (en) * 2014-10-15 2016-04-21 Vincent Suzara Magnetic field structures, field generators, navigation and imaging for untethered robotic device enabled medical procedure
US10037841B2 (en) * 2014-10-15 2018-07-31 Vincent Suzara Magnetic field structures, field generators, navigation and imaging for untethered robotic device enabled medical procedure

Also Published As

Publication number Publication date
EP0181383B1 (de) 1988-10-12
DE3418812A1 (de) 1985-11-21
WO1985005448A1 (en) 1985-12-05
EP0181383A1 (de) 1986-05-21
DE3565605D1 (en) 1988-11-17

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